NATIONAL STANDARD
TCVN 6156 :
1996
PRESSURE
VESSELS - SAFETY ENGINEERING REQUIREMENTS OF ERECTION, USE, REPAIR. TESTING
METHOD
1. Scope and general
provisions
1.1. This Standard applies to pressure vessels
(hereinafter referred to as “vessels”) regulated by the TCVN 6153 : 1996.
1.2. All vessels must undergo technical
inspection arranged by competent authorities before use, during use, and in
case of accidents in accordance with this document.
1.3. Vessels that do not undergo inspection in
a timely manner according to inspection deadline in background sheets, test
records, or use license.
2. Reference standards
TCVN 6153 : 1996 Pressure vessels - Safety
technical requirements pertaining to design, structure, manufacturing.
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TCVN 6155 : 1996, Pressure vessels - Safety
technical requirements pertaining to installation, use, and repair.
3. Inspection of
pressure vessels
3.1. Procedures for inspecting pressure vessels
3.1.1. In respect of new vessels or vessels
entering use for the first time: owners must attach the following technical
dossiers to application for inspection:
a. Background sheet of vessels.
b. Factory release documents of vessels
according to TCVN 6153 : 1996
c. Installation record (in case of fixed vessels),
including the following amendments:
- Name of installation personnel and vessel
owners.
- Characteristics of additional materials in
installation.
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3.1.2. In respect of vessels currently in use,
users must submit documents stating reasons for inspection. Where vessel repair
involves replacement for test purposes, welding, etc. of vessel parts, repair
documents must be included.
3.2. Vessels that have been released from
factory within the last 18 months and have undergone hydraulic tests at
manufacturers, property kept, so transported that they are not damaged, and so
installed that primary parts of the vessels are not welded can be exempted from
hydraulic test for first-time use purpose.
3.3. Vessel owners are responsible for cleaning
vessels prior to inspection and:
a. Partially or entirely dismantling insulating
layers if metal body of vessels are suspected to be damaged.
b. Elevating vessels on the ground where
inspection is difficult.
c. Separating electric heating elements and
moving parts (if applicable).
d. Establishing structures that allow thorough
inspection of vessel parts in respect of vessels that are 2 m in height or
higher.
3.4. Vessel owners must suspend operation to
arrange inspection according to time limit and inform competent authorities 5
days in advance.
3.5. Where competent authorities fail to arrive
in a timely manner, vessel users may establish inspection council.
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3.6. Technical inspection include external
inspection, internal inspection, and hydraulic test.
3.7. External and internal inspection serves:
a. In respect of vessels entering use for the
first time or installed for the first time: determination of technical
conditions of vessels after transportation and installation quality according
to design requirements and compliance with TCVN 6155 : 1996.
b. In respect of periodic or irregular
inspection: determination of technical conditions of vessels after a period of
operation and evaluation of further operating capability.
3.8. During external and internal inspection,
possible defects below must be looked for:
a. Cracks, fissures, deformations, rusts,
corrosions, etc. on vessel body.
b. Imperfect measuring, safety equipment and
instruments.
c. Rusted fastened elements, faulty connections
and insulations which cause metal elements to overheat (for heating vessels),
etc.
Where internal or external protective layer is
damaged, the protective layer must be partially or entirely dismantled so as to
thoroughly examine the damage.
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3.9. Hydraulic test is conducted in order to
examine durability, airtightness, and perfection of certain measuring,
inspection equipment and safety mechanisms.
Components must undergo hydraulic test together
with vessels.
Hydraulic test shall only be conducted after
internal and external examination is satisfactory.
3.10. Interval for periodic inspection:
a. External and internal examination: once
every 3 years;
b. External, internal examination and hydraulic
test: once every six years;
c. Operation test: once every year;
d. Intervals under 3.10.a and 3.10.b reduced by
one-third for vessels containing corrosive substances.
Where manufacturers dictate a shorter
inspection interval, such requirements shall prevail.
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3.11. Hydraulic test pressure of vessels after
installation or during periodic and irregular inspections.
a) In respect of vessels where working
temperature of vessel body reaches 200 oC, test pressure is
compliant with Schedule 1.
Schedule 1
Type of vessel
Permissible working
pressure, kG/cm2
Hydraulic test
pressure, kG/cm2
- Vessels, tanks, or containers (except cast
vessels)
- Vessels, tanks, or containers (except cast
vessels)
- Cast vessels and canisters
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5 or higher
Regardless of pressure
1,5 p and not lower than 2
1,25 p and not lower than 3
1,5 p and not lower than 3
b. In respect of glazed vessels, hydraulic test
pressure shall conform to requirements of manufacturers and shall not be lower
than working permissible working pressure.
c. In respect of vessels where working
temperature of vessel body is between exceeding 200 oC and 400 oC,
test pressure shall not be lower than 1,5 p.
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Vessels must be capable of withstanding test
pressure for 5 minutes after which point pressure is gradually reduced to
working pressure and maintained throughout examination duration.
Vessels shall be categorized as ‘good’ if they
satisfy requirements under 3.4.5 of TCVN 6154 : 1996.
3.12. Cases where irregular inspection is
warranted:
a. Vessels that have been deactivated for 12
months or more are reused;
b. Vessels are renovated, changed in terms of
ownership, or transported for installation at a new location.
c. Vessel deformations are corrected or vessels
undergo repair that involves welding of primary parts of the vessels.
d. Prior to installation of internal protective
layer.
e. Vessel owners or competent authorities
suspect technical conditions of the vessels.
Causes of irregular inspection must be
specified in background sheet of involved vessels.
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3.14. Sulfite cooking vessels and mercury
equipment lined with acid-resistant layer or gas containers for direct
operation with switchgears shall be exempted from hydraulic test, must yield
good results in examination of metal shell and welded connections conducted by
inspecting and measuring externally, and shall undergo ultrasound examination
once every 4 years.
3.15. Where hydraulic test is not feasible due
to stress to foundation, the floor, or the vessel is too significant because of
water mass; difficulty in water discharge; internal layers prohibiting water
intake, hydraulic test can be replaced by gas pressure test (using air or inert
gases) at a similar pressure to hydraulic test.
Gas test shall only be permitted if external
and internal inspection conducted either visually or via non-destructive
methods yields good results.
3.16. Safety measures below must be adopted
during gas test:
a. Valves and pressure gauges on gas supply
pipes must be physically distant from vessel location or outside of rooms in
which vessels are located.
b. During period in which vessels undergo gas
pressure test, unauthorized persons must evacuate to safe locations.
Vessels must be able to withstand test pressure
for 5 minutes after which point the pressure is gradually reduced to working
pressure at which point connections are examined for airtightness via the use
of soap solution or other methods.
Do not use test hammer during gas pressure
tests.
3.17. Vessel owners must conduct additional
inspections periodically as follows:
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b. In respect of vessels that operate with
corrosive substances: once every year or after each repair and maintenance. Following
internal and external examination, gas pressure test (using either air or inert
gas) shall be conducted at working pressure of the vessels.
4. Inspection of tanks,
gas containers and canisters
4.1. Tanks and containers must undergo periodic
inspection at gas refilling facilities. Propane - butane tanks or containers
can undergo inspection at repair stations of using entities.
Interval of periodic inspection of tanks and
containers of liquefied gas:
a. Tanks and containers of substances that are
corrosive to metal (chlorine, hydrogen sulfide, etc.): at least once every 2
years.
b. Tanks and containers of propane - butane,
and conventional substances: at least once every 4 years.
c. Vacuum-jacketed vessels (for refrigerant):
at least once every 6 years.
4.2. All new canisters shall, prior to being
filled with gas for the first time, undergo inspection conducted by competent
authorities in a manner compliant with 5% rule. Where one of the inspected canisters
does not satisfy technical requirements, each canister in a batch must be
inspected. Where inspected canisters satisfy requirements, competent
authorities shall issue circulation license.
4.3. Periodic inspection of canisters shall be
conducted by refilling facilities or canister testing stations.
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a. have adequate, convenient, and safe testing
locations.
b. be adequately outfitted with equipment and
instruments for inspection purposes.
c. have canister inspection procedures.
d. employ inspection personnel who are
professionally qualified and assigned in writing.
Upon issuance of license to inspect canisters,
competent authorities must register steel seals and signature that gas
refilling facilities or canister testing stations mark canisters with.
4.5. Canister inspection shall take place in
separate rooms outfitted with special safety equipment where ambient
temperature must not be lower than 12 oC and lighting for internal
inspection is powered by a power source of at most 12 V.
For the purpose of inspecting canisters of
explosive gas, parts of hand-held lights and electrical equipment must be
explosion-proof.
4.6. Canisters in use must undergo periodic
inspection at least once every 5 years. Canisters of corrosive gas (chlorine, chloromethane,
black phosphorus, hydrogen sulfide, sulfur dioxide, hydrogen chloride, etc.); canisters
of compressed gas or liquefied gas used as vehicle fuel must undergo periodic
inspection at least once every 2 years.
Where inspection interval set by manufacturers
is shorter than periodic inspection interval, the interval regulated by
manufacturers shall prevail.
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- External and internal inspection.
- Weight and volume determination.
- Hydraulic test.
Mass and volume examination shall only be
conducted to seamless canisters.
Prior to inspection, canisters must be cleaned
thoroughly. If necessary, gas purging shall be implemented. Canisters of which
neck rings are loosened or not properly seated must be rectified prior to
inspection.
4.8. During internal and external inspection,
canisters with the following defects must be discarded:
- Cracks
- Flaked shells.
- Bulging or concaved shell.
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- Threads of canister neck are corroded or
damaged.
- Control markings are not properly engraved.
4.9. Volume of a canister is determined by
subtracting weight of the empty canister from that of the canister filled with
water. Other reliable methods for determining canister volume are acceptable.
4.10. Where seamless canisters (12 to 55 liters
in volume) suffer from excessive weight reduction or volume increase, working
pressure must be reduced according to Schedule 2.
Schedule 2
Weight reduction, %
Volume increase, %
Conclusion
7,5 to 10
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Exceeding 10 to 15
Exceeding 15 to 20
Exceeding 20
1,5 to 2
Exceeding 2 to 2,5
Exceeding 2,5 to 3
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- Allow reaching 85% the initial permissible
pressure
- Allow reaching 50% the initial permissible
pressure
- Allow working at pressure of 6 kG/cm2
or lower.
- Discard
4.11. Engraved information on weight, volume,
and working pressure must be available on shell of canisters with reduced
working pressure. Old figures must be marked with double crosses.
4.12. As soon as inspection results are
available, the following figures must be engraved on canister body:
- Seal of inspecting person (entity);
- Date of inspection and date of next
inspection (on the same row as seal of inspecting person (entity)).
The following figures must be recorded in
inspection records:
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b. Canister code; manufacturing country.
c. Manufacturing number; date of manufacturing.
d. Inspection date and next inspection date.
e. Weight of canister engraved by manufacturer,
kg.
f. Weight of canister determined in inspection,
kg.
g. Volume of canister engraved by manufacturer.
h. Volume determined in inspection.
i. Permissible working pressure, kG/cm2.
k. Test pressure, kG/cm2.
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m. Signature of inspecting person.
n. Confirmation of chief technician and
figurehead.
4.13. Discarded canisters must have threads of
their neck ring destroyed or shells drilled so that they cannot be mistaken as canisters
to be refilled with gas.
4.14. Filled canisters shall be kept in storage
units, upon periodic inspection, personnel in charge of storage shall arrange
inspection compliant with 5% rule. Where inspected canisters satisfy inspection
requirements, other canisters can remain in storage for up to one more year. Where
inspected canisters do not satisfy requirements, use or completely deplete gas
contents in order to conduct technical inspection of each canister.
These canisters must be used or depleted within
one month from the date on which unsatisfactory inspection results are
produced.
5. Vessel incident
investigation
5.1. Vessel incidents that warrant irregular
technical inspection shall require investigation to determine causes and
solutions.
Investigation shall be conducted by councils
established in accordance with decision of competent authorities where one of
the council members must be occupational safety authorities.
Where incidents cause harm to humans,
declaration and investigation shall conform to applicable regulations on
declaration and investigation of occupational accidents.
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